An oxygen sensor may include a heater to operate the oxygen sensor within a desirable temperature range where output of the oxygen sensor may reliably reflect conditions within an exhaust system of an engine. If a voltage that is applied to the heater to control oxygen sensor temperature is too high or too low, output of the oxygen sensor may be less accurate than is desired. Consequently, an engine air-fuel ratio may be leaner or richer than is desired and conversion efficiency of exhaust after treatment devices may degrade. A voltage that is applied to the oxygen sensor's heater when the oxygen sensor is new to operate the oxygen sensor at a desired temperature may cause the same oxygen sensor to operate outside of a desired temperature range after the oxygen sensor has aged. Therefore, it may be desirable to provide a way of controlling oxygen sensor temperature so that the oxygen sensor operates in a desired temperature range even after the oxygen temperature sensor has aged.
The inventors herein have identified methods and systems that compensate for oxygen sensor electrode aging. In particular, the inventors have developed an operating method for an oxygen sensor, comprising: adjusting a voltage applied to an oxygen sensor heater while the oxygen sensor is exposed to combustion products of a first rich air-fuel mixture according to a first curve describing a relationship between oxygen sensor electrode impedance and oxygen sensor electrode temperature for the oxygen sensor being exposed to the combustion products of a second lean air-fuel mixture.
By adjusting a voltage applied to an oxygen sensor heater according to a first curve describing a relationship between oxygen sensor electrode impedance and oxygen sensor electrode temperature for the oxygen sensor being exposed to combustion products of a rich air fuel mixture, it is possible to provide the technical result of improved oxygen sensor temperature control. For example, the voltage that is applied to the oxygen sensor heater may be adjusted responsive to a requested oxygen sensor electrode impedance (Ri) for control, and the requested oxygen sensor electrode impedance (Ri) for control may be determined from curves describing relationships between oxygen sensor temperature and oxygen sensor electrode impedance during rich and lean exhaust gas conditions. As the oxygen sensor electrode impedance changes as the oxygen sensor ages, the requested oxygen sensor electrode impedance (Ri) for control may be revised so that the voltage applied to the oxygen sensor heater may be adjusted so as to operate the oxygen sensor electrode in a desired temperature range. As a result, the output of the oxygen sensor may be made more consistent as the oxygen sensor ages.
The present description may provide several advantages. In particular, the approach may improve engine air-fuel control and reduce engine emissions. Further, the approach does not require extensive oxygen sensor characterization to determine oxygen sensor operating characteristics at all stages of oxygen sensor life. Further still, the approach may be selectively activated to reduce controller computational load.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.